High strength, high capacity filter media and structure

ABSTRACT

In the filtration of fluid materials, the removal of particulate from the moving stream requires substantial pressure to maintain flow and substantial capacity for removing particulate. The filters of the invention are rugged, high wet strength materials having a basis weight, permeability and efficiency suitable to obtain substantial reduction in particulate loading from liquid streams without plugging or mechanical failure. In particular, the filters of the invention permit the removal of substantial proportions of particulate from non-aqueous streams including lubricant oils, hydraulic fluids and other contaminated streams.

FIELD OF THE INVENTION

The invention relates to a filtration medium and a filter using themedium. The medium has high strength, efficiency and high capacity forfiltration of particulate from a stream. The filter medium or mediacomprise a non-woven web suitable for removal of particulate from mobilefluids such as aqueous streams and non-aqueous streams including fuels,lubricating oils and hydraulic fluids. The invention relates tonon-woven media layers obtaining sufficient wet strength, particulateefficiency, permeability and other properties to survive the commonoperating conditions, such as variation in flow rate, temperature,pressure and particulate loading while removing substantial particulateloads from the liquid stream. The invention further relates to filterstructures comprising one or more layers of the particulate removingmedia with other layers of similar or dissimilar media. These layers canbe supported on a porous or perforate support and can provide mechanicalstability during filtering operations. Lastly, the invention relates toa method of filtering both aqueous and non-aqueous fluids.

BACKGROUND OF THE INVENTION

Non-woven webs have been manufactured for many years for many end uses,including filtration media. Such structures made from bicomponent orsheath-core materials are disclosed in, for example, Wincklhofer et al.,U.S. Pat. No. 3,616,160; Sanders, U.S. Pat. No. 3,639,195; Perrotta,U.S. Pat. No. 4,210,540; Gessner, U.S. Pat. No. 5,108,827; Nielsen etal., U.S. Pat. No. 5,167,764; Nielsen et al., U.S. Pat. No. 5,167,765;Powers et al., U.S. Pat. No. 5,580,459; Berger, U.S. Pat. No. 5,620,641;Berger, U.S. Pat. No. 6,174,603; Hollingsworth et al., U.S. Pat. No.6,146,436; Dong, U.S. Pat. No. 6,251,224; Sovari et al., U.S. Pat. No.6,355,079; Hunter, U.S. Pat. No. 6,419,721; Cox et al., U.S. Pat. No.6,419,839; Stokes et al., U.S. Pat. No. 6,528,439; Amsler, U.S. Pat. No.H2,086 and Amsler, U.S. Pat. No. 6,267,252. Such structures have beenmade by both air laid and wet laid processing and have been used in bothair and liquid filtration applications with some degree of success. Inthis regard we have found that the previous non-woven webs that are usedfor particulate removal from mobile fluids often suffer from a lack ofmechanical strength and short useful life when wet by liquid underfiltration condition. Often the pressure of the fluid exceeds the wetburst strength of the media. The media can also become rapidly pluggedand reduced in permeability causing reduced flow or failure of fluidmovement. Burst or plugged media rapidly fail to filter particulate. Aburst media would fail to protect the equipment from particulate it wasdesigned to protect. Substantially increased or high pressure drop wouldrestrict the fluid flow resulting in loss of fluid flow and power

Many attempts to obtain non-woven structures with suitable perforate orporous supports have been attempted. Melt blown materials and thermallamination techniques have been attempted, however, the resultingstructures often obtain incorrect pore sizes, reduced efficiency,reduced permeability, lack of strength or other problems rendering themedia or filter structure insufficient for useful filtrationapplications.

A substantial need exists for filtration media, filter structures andfiltration methods that can be used for removing particulate materialsfrom liquid compositions, such as aqueous liquids and in particular,non-aqueous liquids such as fuels, lubricating oils and hydraulicfluids. The invention provides such media, filtration structures andmethods and provides a unique media or media layer combinations thatachieve substantial permeability, high wet strength, substantialefficiency and long filtration life.

BRIEF DESCRIPTION OF THE INVENTION

We have found a filter media and a unique filter structure capable ofremoving particulate from liquid streams. The media comprises athermally bonded sheet made by combining a substantial proportion of aninorganic glass fiber, a fiber blend of differing fiber diameters, and abicomponent thermoplastic binder fiber. Such a medium can be made withoptimal secondary fibers and other additive materials. These componentscombine to form a filter medium or non-woven material having substantialflow capacity, permeability and high strength. The media of theinvention can maintain intact filtration capacity at high pressure for asubstantial period of time. The media and filter operate at substantialflow rate, high capacity and substantial efficiency.

A first aspect of the invention comprises a filtration media or mediumhaving a thermally bonded non-woven structure.

A second aspect of the invention comprises a bilayer filtration mediumor media comprising at least one loading layer and at least oneefficiency layer with the mobile fluid passing first through the loadinglayer.

A third aspect of the invention comprises a filter structure comprisinga filtration media of the invention, a loading layer filtration media ofthe invention, an efficiency layer filtration media of the invention orcombinations thereof also combined with other filtration layers, supportstructures and other filter components.

A fourth aspect of the invention comprises a depth loading layer thatcan be used as a stand alone layer or as a combination with anefficiency layer. The depth layer can be responsible for a large part ofthe high performance character of this media, where the depth loadingmedia that does not compress or tear when subjected to applicationconditions

Lastly, a fifth aspect of the invention comprises a method of filteringthe mobile liquid phase having a particulate load using the filtrationaspects of the invention.

In general, the technology can be applied to filtering liquid systems.In liquid filtering techniques, the collection mechanism is believed tobe sieving. In a single layer the efficiency is that of the layer. Thecomposite efficiency in a liquid application is limited by theefficiency of the single layer with the highest efficiency. The liquidswould be directed through the media according to the invention, withparticulates therein trapped in a sieving mechanism. In liquid filtersystems, i.e. wherein the particulate material to be filtered is carriedin a liquid, such applications include aqueous and non-aqueous and mixedaqueous/non-aqueous applications such as water streams, lube oil,hydraulic fluid, fuel filter systems or mist collectors. Aqueous streamsinclude natural and man-made streams such as effluents, cooling water,process water, etc. Non-aqueous streams include gasoline, diesel fuel,petroleum and synthetic lubricants, hydraulic fluid, brake fluid andother ester based working fluids, cutting oils, food grade oil, etc.Mixed streams include dispersions comprising water in oil and oil inwater compositions and aerosols comprising water and a non-aqueouscomponent.

A substantial proportion of glass fiber is used in the manufacture ofthe media of the invention. The glass fiber provides pore size controland cooperates with the other fibers in the media to obtain a media ofsubstantial flow rate, high capacity and substantial efficiency. Theterm glass fiber “source” means a glass fiber composition characterizedby an average diameter and aspect ratio that is made available as adistinct raw material. Blends of fiber obtained from such sources thatvary in diameter do not read on single source.

Other fibers called “secondary fibers” can also be used in themanufacture of the media layer of the invention. Secondary fibers aresingle component fibers that add some aspect of layer formation orfilter property to the medium. Such secondary fibers can add to thefiltration properties of the invention, but it can also act as “binderfibers” in binding the fibrous mat into a useful media web. These fiberscan add to the filtration characteristic of the media or can add to thebinder characteristic of the bicomponent fiber. The term “secondaryfibers” can include a variety of different fibers from natural syntheticor specialty sources. Secondary fibers are typically monocomponentfibers with a diameter that can range from about 0.1 to about 100micrometers and can be made from a variety of materials includingnaturally occurring cotton linters wool, various cellulosic andproteinaceous natural fibers, synthetic fibers including rayon, acrylic,aramide, nylon (including nylon 6, nylon 6,6, nylon 6,12, etc.),polyolefin (including polyethylene's, polypropylenes), polyester fibers(including polyethylene terephthalate, polybutylene terephthalate, PCT,etc). Additionally, the binder fiber can include fibers made from suchpolymers as polyvinyl chloride, polyvinyl alcohol. Secondary fibers canalso include inorganic fibers such as carbon/graphite fiber, metalfiber, ceramic fiber and combinations thereof.

The preferred filter structure of the invention comprises at least onefiltration media layer of the invention supported on a mechanicallystable perforate support structure. The filtration layer can comprisetwo media layers, a loading layer and an efficiency layer, of theinvention with cooperating functions to achieve excellent particulateremoval at high efficiency. While the differences between the loadingand efficiency layers can be difficult to separate when made in serialfashion, we believe that the layers have the following general andpreferred characteristics. TABLE 1 General Characteristics Weight Perm,Thickness Loading Description Lbs/3000 ft² Ft-min⁻¹ Inches gms/ft² β_(x)= 75 μm Efficiency layer 15-50 5-50 0.01-0.02 12  9 Loading layer 25-5040-200 0.015-0.025 23 12 Laminated composite  50-150 5-50 0.04-0.05 17 9 Nw loading layer 25-50 50-125 0.01-0.02 — — New efficiency layer50-75 10-45  0.02-0.04 13 10 New composite  50-150 10-50  0.025-0.055 1911

TABLE 2 Preferred Characteristics Weight Perm, Thickness LoadingDescription Lbs/3000 ft² Ft-min⁻¹ Inches gms/ft² β_(x) = 75 μmEfficiency layer 40-50 20-40 0.01-0.02 12  9 Loading layer 35-45 120-1400.015-0.025 23 12 Laminated composite 100-125 15-35 0.04-0.05 17  9 Nwloading layer 30-40 100-140 0.01-0.02 — — New efficiency layer 50-7520-40 0.02-0.04 13 10 New composite  75-127 15-40 0.025-0.055 19 11

TABLE 3 Specific Characteristics Weight Perm, Thickness LoadingDescription Lbs/3000 ft² Ft-min⁻¹ Inches gms/ft² β_(x) = 75 μmEfficiency layer 42 28 0.018 12  9 Loading layer 40 135 0.022 23 12Laminated composite 110 21 0.045-0.050 17  9 Nw loading layer 35 1150.015-0.020 — — New efficiency layer 65 30 0.03  13 10 New composite 10022 0.05‘ 19 11

The perforate structure supports the media under the influence of fluidunder pressure passing through the media. The filter structure of theinvention can also be combined with additional layers of the perforatesupport, high permeability mechanically stable scrim and additionalfiltration layers such as a loading layer. This multilayer mediacommonly is housed in a filter cartridge commonly used in the filtrationof non-aqueous liquids.

“Bicomponent fiber” means a thermoplastic material having at least onefiber portion with a melting point and a second thermoplastic portionwith a lower melting point. The physical configuration of these fibersis typically in a “side-by-side” or “Sheath-core ” structure. Inside-by-side structure, the two resins are typically extruded in aconnected form in a side-by-side structure. In the sheath-corestructure, the low melting point (about 100 to 120° C. thermoplastic istypically extruded around a fiber of the higher melting typically over240° C.) point material. The lower melting polymer acting as athermoplastic binding agent, the melt polymer adhering the component andthe higher melting thermoplastic acting as a structural material. Inuse, the bicomponent fibers typically have a fiber size or diameter ofabout 10 to 20 micrometers and are typically in a fiber form having alength of about 6 to about 12 mm, preferably about 6 mm. Thecross-sectional structure of such fibers can be, as discussed above, the“side-by-side” or “sheath-core” structure or other structures thatprovide the same thermal bonding function. The value of the bicomponentfiber is that the relatively low molecular weight resin can melt undersheet forming conditions to act to bind the bicomponent fiber, and otherfibers present in the sheet making material into a mechanically stablesheet. Typically, the polymers of the bicomponent (Sheath-core andside-by-side) fibers are made up of different thermoplastic materials,such as for example, polyolefin/polyester (Sheath-core) bicomponentfibers whereby the polyolefin, e.g. polyethylene sheath, melts at atemperature lower than the core, e.g. polyester. Typical thermoplasticpolymers include polyolefins, e.g. polyethylene, polypropylene,polybutylene, and copolymers thereof, polytetrafluoroethylene,polyesters, e.g. polyethylene terephthalate, polyvinyl acetate,polyvinyl chloride acetate, polyvinyl butyral, acrylic resins, e.g.polyacrylate, and polymethylacrylate, polymethylmethacrylate,polyamides, namely nylon, polyvinyl chloride, polyvinylidene chloride,polystyrene, polyvinyl alcohol, polyurethanes, cellulosic resins, namelycellulosic nitrate, cellulosic acetate, cellulosic acetate butyrate,ethyl cellulose, etc., copolymers of any of the above materials, e.g.ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers,styrene-butadiene block copolymers, Kraton rubbers and the like.Particularly preferred in the present invention is a bicomponent fiberknown as 271P available from DuPont. Others fibers include FIT 201,Kuraray N720 and the Nichimen 4080. All of these demonstrate thecharacteristics of cross-linking the sheath poly upon completion offirst melt. This is important for liquid applications where theapplication temperature is typically above the sheath melt temperature.If the sheath does not fully crystallize then the sheath polymer willremelt in application and coat or damage downstream equipment andcomponents.

“Glass fiber” is fiber made using glass of various types. The glassfibers used in papers of the present invention include glass types knownby the designations: A, C, D, E, Zero Boron E, ECR, AR, R, S, S-2, N,and the like, and generally, any glass that can be made into fiberseither by drawing processes used for making reinforcement fibers orspinning processes used for making thermal insulation fibers. Such fiberis typically used as a collection of fiber of diameter about 0.1 to 10micrometers and an aspect ratio (length divided by diameter) of about 10to 10,000.

We have found that by blending various proportions that substantiallyimproved permeability can be obtained by blending various fiberdiameters. Typically, glass fibers produced in a product having a fiberdiameter within a certain range of variation. We have found thatblending various (average fiber diameter) sizes of fibers, about 0.1 toabout 1 micron, about 0.3 to 2, about 0.5 to 3 about 0.75 to 5 or about3 to 10 micrometers, can result in high permeability and excellent flow.The term blend in this context means that the medium contains at leastsome of at least two different fiber sources of differing dimensionstypically different diameters.

Some amount of a resinous binder component is necessary to obtainadequate strength for the non-woven media of this invention. Resin usedas binder can be in the form of water soluble or dispersible polymeradded directly to the paper making dispersion or in the form ofthermoplastic binder fibers of the resin material intermingled with thearamide and glass fibers to be activated as a binder by heat appliedafter the non-woven is formed. Dispersing the fibers and then adding thebinder material or dispersing the binder material and then adding thefibers comprise two processes for dispersion formation. Combining adispersion of fibers with a dispersion of the binder material can also,make the dispersion. The concentration of fibers in the dispersion canrange from 0.01 to 1 weight percent based on the total weight of thedispersion. The concentration of binder material in the dispersion canrange from 5 to 50 weight percent based on the weight of the fibers;and, if the binder material is fibrids, the concentration can range from15 to 35 weight percent based on the total weight of the paper.

Wet laid or dry laid processes can be used. In making the media of theinvention, a fiber mat is formed using either wet or dry processing. Themat is heated to form the media by internally adhering the fibers. Thebicomponent fiber used in the media of the invention permits the fiberto fuse into a mechanically stable mass. The bicomponent fiber having athermally bonding exterior sheath causes the bicomponent fiber to bindwith other fibers in the media layer. The bicomponent fiber cooperateswith the aqueous resin and other fibers to form the medium.

Such a medium typically comprises a thin layer with substantialfiltration properties. In many applications, especially those involvingrelatively high flow rates, an alternative type of filter media,sometimes generally referred to as “depth” media, can be used. A typicaldepth media comprises a relatively thicker tangle of fibrous materialthan standard media. Depth media is generally defined in terms of itsporosity, density or percent solids content. For example, a 2-3%solidity media would be a depth media mat of fibers arranged such thatapproximately 2-3% of the overall volume comprises fibrous materials(solids), the remainder being air or gas space. Another useful parameterfor defining depth media is fiber diameter. If percent solidity is heldconstant, but fiber diameter (size) is reduced, pore size is reduced;i.e. the filter becomes more efficient and will more effectively trapsmaller particles. A typical conventional depth media filter is a deep,relatively constant (or uniform) density, media, i.e. a system in whichthe solidity of the depth media remains substantially constantthroughout its thickness. By “substantially constant” in this context,it is meant that only relatively minor fluctuations in density, if any,are found throughout the depth of the media. Such fluctuations, forexample, may result from a slight compression of an outer engagedsurface, by a container in which the filter media is positioned. Ingeneral, a depth media arrangement can be designed to provide “loading”of particulate materials substantially throughout its volume or depth.Thus, such arrangements can be designed to load with a higher amount ofparticulate material, relative to surface-loaded systems, when fullfilter lifetime is reached. However, in general the tradeoff for sucharrangements has been efficiency, since, for substantial loading, arelatively low solids media is desired. Gradient density systems such asthose in the patents referred to above, have been designed to providefor substantial efficiency and longer life. In some instances,surface-loading media is utilized as a “polish” filter in sucharrangements. In the preferred wet laid processing, the medium is madefrom an aqueous furnish comprising a dispersion of fibrous material inaqueous medium. The aqueous liquid of the dispersion is generally water,but may include various other materials such as pH adjusting materials,surfactants, defoamers, or other processing aids and the like. Theaqueous liquid is usually drained from the dispersion by conducting thedispersion onto a screen or other perforated support retaining thedispersed solids and passing the liquid to yield a wet papercomposition. The wet composition, once formed on the support, is usuallyfurther dewatered by vacuum or other pressure forces and further driedby evaporating the remaining liquid.

The media of this invention can be made on equipment of any scale fromlaboratory screens to commercial-sized papermaking machinery such asFourdrinier, inclined wire, and cylinder wire machines, and combinationsof them. The general process involves making a dispersion of fibers,glass fibers, and binder material in an aqueous liquid, draining theliquid from the dispersion to yield a wet composition, and heating thewet composition to both dry and thermally bond the fiber into a layer toform the useful medium. This can be done in one step or a series ofsteps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows in graphical data our experience in the use of bicomponentfibers in filtration media. The use of bicomponent fiber (all othervariables being held constant) provides substantial increase infiltration capacity of the media of the invention, the media maintainingsubstantial mechanical strength.

FIG. 2 shows an increase in effective particulate loading resulting fromthe use of a bicomponent fiber

FIG. 3 shows an increase in effective particulate loading resulting fromthe use of a bicomponent fiber in a resin saturated media.

FIG. 4 shows multipass results of similar hand sheets that can be resinsaturated or resin free.

FIG. 5 is a cross section of a spin on cartridge filter aspect of theinvention using a pleated media layer for filtering liquids.

FIG. 6 is a cross sectional top view of the pleated media of theinvention supported by a perforate metal support. This combination isone aspect of the supported media of the invention.

FIG. 7 shows a side view of the down flow side of a pleated media of theinvention supported by a screen support.

DETAILED DESCRIPTION OF THE INVENTION

The medium or media of the invention relates to a composite, non-woven,air laid or wet laid material having formability, stiffness andrigidity, and mechanical stability for filtration properties; highparticulate loading capability, low pressure drop during use and a poresize and efficiency suitable for use in filtering fluids. Preferably,the filtration media of the invention is typically wet laid and is madeup of randomly oriented array of media fiber and bicomponent fiber thatare bonded together using the bicomponent binder fiber and the binderresin of the invention. Heat is used to activate the thermoplasticbinding agents in the binder fiber and the resin. The media that can beused in the filters and methods of the invention contain a media fiber,a bicomponent binder fiber, a binder and other components. The medium ormedia can be formed into substantially planar sheets or formed into avariety of geometric shapes using forms to hold the wet compositionduring thermal bonding. The media fiber of the invention includes glass,metal, silica and other related fibers. The preferred fiber for use inthe invention is a glass fiber having an aspect ratio of 10 to 10,000and a diameter that can range from about 0.1 to about 10 micrometers indiameter while preferred materials are blends of glass fiber ofdiffering dimensions.

The filter media of the present invention is typically suited for highefficiency filtration properties such that liquids, including aqueousand non-aqueous fuel, lubricant, hydraulic or other such fluids can berapidly filtered to remove contaminating particulates.

We have found that two filter media of this description can be combined,a loading layer and an efficiency layer, each of said layers havingdistinct structures and filtration properties to form a composite layer.The layers are distinct structures with different filtration propertiesthat cooperate to obtain filtration performance. In the manufacturingprocess is formed the efficiency layer first, allowing more of the finerglass fibers to deposit on the efficiency or wire side of the medium.This aids in forming a gradient structure for improved loadingperformance. The loading layer is then formed on top of the efficiencylayer. Preferably before the efficiency layer is completely formed. Thisallows some intermingling of the fibers between the two layers, forminga gradient structure and enhancing the strength and bond between thelayers. When adding the loading layer you also allow the finer fibers tomore intermingle with the efficiency layer. When forming the efficiencylayer some of the finest fibers are lost through the forming screen orwire. When you form the loading layer, you loose very few of the finestfibers because they are captured and intermingled with the originalefficiency layer. The performance, both filtration and physicalproperties, of sheets formed together vs formed separately and laid ontop of each other are different. The efficiency layer is a highlyefficient layer having suitable porosity efficiency permeability andother filtration characteristics to remove any remaining harmfulparticulate from the fluid stream as the fluid passes through the filterstructure. The loading filtration media of the invention has a basisweight of about 33 to about 65 g-m⁻². The efficiency layer has a basisweight of about 65 to about 130 g-m⁻². The efficiency layer has a meanflow pore size smaller than the loading layer that ranges from about 2to about 10 micrometers. The loading layer has a permeability thatranges from about 80 to 160 ft-min⁻¹. The efficiency layer has apermeability of about 10 to 50 ft-min⁻¹. The loading layer or theefficiency layer of the invention has a wet bursting strength of greaterthan about 5 psi, typically about 10 to about 30 psi. The combinedfiltration layer has a permeability of about 15 to 40 ft-min⁻¹, a wetburst strength of 10 to 30 psi and a basis weight of 130 to 200 g-m⁻².Microfiber glass is not coated or sized. Only large chopped glass issized. Both types are used in this application. These commerciallyavailable fibers are characteristically coated or sized with a sizing.Such coatings cause the otherwise ionically neutral glass fibers to formand remain in bundles. Manufacturers of glass fibers commonly employsizes such as this. The sizing composition and cationic antistatic agenteliminates fiber agglomeration and permits a uniform dispersion of theglass fibers upon agitation of the dispersion in the tank. Blends ofglass fibers can substantially aid in improving permeability of thematerials. We have found that combining two or more sources of glassfiber having an average particle size of about 0.3 to 0.5 micron, glassfiber having an average particle diameter of about 1 to 2 micron, glassfiber having an average particle diameter of about 3 to 6 micrometers orglass fiber with a particle diameter of about 6 to 10 micrometers invarying proportions can substantially improve permeability. We believesuch glass fiber blends obtain a controlled pore size resulting in adefined permeability in the media layer.

Binder resins can typically comprise solvent based, water soluble orwater sensitive polymer materials. Water based latex as the saturateresin. One could easily use solvent based resins such as phenols andepoxy phenolic blends just as easily. Polymer materials are typicallyprovided in either dry form or aqueous dispersions. Such useful polymermaterials include acrylic polymers, ethylene vinyl acetate polymers,ethylene vinyl polyvinyl alcohol, ethylene vinyl alcohol polymers,polyvinyl pyrrolidone polymers, and natural gums and resins useful inaqueous solution. Various combinations of polymers for the bicomponentfiber may be useful in the present invention, but it is important thatthe first polymer component melt at a temperature lower than the meltingtemperature of the second polymer component and typically below 300° F.Further, the bicomponent fibers are integrally mixed and evenlydispersed with the pulp fibers. Melting of the first polymer componentof the bicomponent fiber is necessary to allow the bicomponent fibers toform a tacky skeletal structure, which upon cooling, captures and bindsmany of the pulp fibers, as well as binds to other bicomponent fibers.The bicomponent fiber used in the media of this invention generally havea length of 0.1 to 10 millimeters and a diameter of 10 to 20micrometers.

The preferred materials for the water soluble or dispersible binderpolymer are water soluble or water dispersible thermosetting resins suchas acrylic resins. methacrylic resins, polyamide resins, epoxy resins,phenolic resins, polyureas, polyurethanes, melamine formaldehyde resins,polyesters and alkyd resins, generally, and specifically, water solubleacrylic resins. methacrylic resins, polyamide resins, that are in commonuse in the papermaking industry. Such thermoplastic binder resinmaterials are typically aqueous dispersions of vinyl thermoplasticresins including vinyl acetate materials, vinyl chloride resins,polyvinyl alcohol resins, polyvinyl acetate resins, polyvinyl acetylresins, acrylic resins, methacrylic resins, polyamide resins,polyethylene vinyl acetate copolymer resins, thermosetting resins suchas urea phenol, urea formaldehyde, melamine, epoxy, polyurethane,curable unsaturated polyester resins, polyaromatic resins, resorcinolresins and similar elastomer resins. Such binder resins typically coatthe fiber and adhere fiber to fiber in the final non-woven matrix.Sufficient resin is added to the furnish to fully coat the fiber withoutcausing film over of the pores formed in the sheet material. The resincan be added to the furnish during papermaking or can be applied to themedia after formation.

The latex binder, used to bind together the three-dimensional non-wovenfiber web in each non-woven layer or used as the additional adhesive,can be selected from various latex adhesives known in the art. Theskilled artisan can select the particular latex adhesive depending uponthe type of fibers that are to be bound. The latex adhesive may beapplied by known techniques such as spraying, foaming, curtain coating,gravure rolling or size pressing saturation techniques. The amount ofsolids in the latex adhesive used depends, inter alia, on the weight ofthe fibers in each layer. Generally, latex adhesives having from 15 to25% solids are used.

Non-woven media of the invention can contain fibers made from a numberof both hydrophilic and hydrophobic fibers. These fibers cooperate withthe glass fiber and the bicomponent fiber to form a mechanically stable,but strong, permeable filtration media that can withstand the mechanicalstress of the passage of fluid materials and can maintain the loading ofparticulate during use. The fiber characteristics are typicallyexpressed as denier, typically is considered to indicate the weight ingrams of 9000 meters of fiber.

The secondary thermoplastic fibers include, but are not limited to,polyester fibers, polyamide fibers, polypropylene fibers,copolyetherester fibers, polyethylene terephthalate fibers, polybutyleneterephthalate fibers, polyetherketoneketone (PEKK) fibers,polyetheretherketone (PEEK) fibers, liquid crystalline polymer (LCP)fibers, and mixtures thereof. Polyamide fibers include, but are notlimited to, nylon 6, 66, 11, 12, 612, and high temperature “nylons”(such as nylon 46) including cellulosic fibers, polyvinyl acetate,polyvinyl alcohol fibers (including various hydrolysis of polyvinylalcohol such as 88% hydrolyzed, 95% hydrolyzed, 98% hydrolyzed and 99.5%hydrolyzed polymers), cotton, viscous rayon, thermoplastic such aspolyester, polypropylene, polyethylene, etc., polyvinyl acetate,polylactic acid, and other common fiber types. The thermoplastic fibersare generally fine (about 0.5-20 denier), short (about 0.1-5 cm), staplefibers, possibly containing precompounded conventional additives, suchas antioxidant, stabilizers, lubricants, tougheners, etc. In addition,the thermoplastic fibers may be surface treated with a dispersing aid.The preferred thermoplastic fibers are polyamide and polyethyleneterephthalate fibers, with the most preferred being polyethyleneterephthalate fibers.

The sheet media of the invention are typically made using papermakingprocesses. The media can be planar or can be made in various geometricforms. Such wet laid processes are particularly useful and many of thefiber components are designed for aqueous dispersion processing.However, the media of the invention can be made by air laid processesthat use similar components adapted for aid laid processing. Themachines used in wet laid sheet making include hand laid sheetequipment, Fourdrinier papermaking machines, cylindrical papermakingmachines, inclined papermaking machines, combination papermakingmachines and other machines that can take a properly mixed paperfurnish, form a layer of the furnish components, remove the fluidaqueous components to form a wet sheet. A fiber slurry containing thematerials are typically mixed to form a uniform fiber slurry. The fiberslurry is then subjected to a wet laid papermaking process. Once theslurry is formed into a wet laid sheet, the wet laid sheet can then bedried, cured or otherwise processed to form a dry permeable, but realsheet or medium. Once sufficiently dried and processed to filtrationmedia, the sheets are typically about 0.01 to 0.1 or 0.02 to 0.08 inchin thickness, having a basis weight of about 30 to 250 g-m-². For acommercial scale process, the bicomponent mats of the invention aregenerally processed through the use of papermaking-type machines such ascommercially available Fourdrinier, wire cylinder, Stevens Former, RotoFormer, Inver Former, Venti Former, and inclined Delta Former machines.Preferably, an inclined Delta Former machine is utilized. A bicomponentmat of the invention can be prepared by forming bicomponent fiber andmedia or glass fiber slurries and combining the slurries in mixingtanks, for example. The amount of water used in the process may varydepending upon the size of the equipment used. The furnish may be passedinto a conventional head box where it is dewatered and deposited onto amoving wire screen where it is dewatered by suction or vacuum to form anon-woven bicomponent web. The web can then be coated with a binder byconventional means, e.g., by a flood and extract method or roll coatingtechniques and passed through a drying oven that dries the mat and curesthe binder and thermally bonds the sheet or medium. The resulting matmay be collected in a large roll.

Synthetic especially polyester and glass fiber multi-layer filtrationmedia can be made using both bi-component PET/PET as well as monomer PVAbinder fiber and acrylic latex resin. Both efficiency and loading layersare formed nearly simultaneously on a paper machine. Filtration media issuitable for mobile and in-plant hydraulic applications as well asmobile equipment lube oil applications.

Experimental The Description of the Hand Sheet Making Procedure

Eight experimental 12 inch by 12 inch size hand sheets were made usingthe furnish recipes in Table 3 using the following procedure.

Procedure:

The materials were selected and weight them into individual containers.For example, to make one batch of 12 inch by 12 inch size hand sheets,76 grams of select fibers or fibers (depends on the furnishrequirements) is used. The fibers were dispersed in known quantity ofwater, using a blender. If there is insufficient capacity in the blenderto disperse all of the fibers in one batch at a time, sub-divide thebatch into more manageable parts, with enough sulfuric acid, to reducepH to about 2.5 to aide dispersion and improve the final formation ofthe filter media. Combine all parts of fiber dispersion in onecontainer, and then add additional water keeping careful account ofquantity of water used to reach a final sheet forming consistency(typically about 0.05%), then stir sufficiently to get uniformdispersion, 15 minutes should be sufficient, before hand sheetformation. This method ensures that a known consistency (fiber weight towater volume of material) is obtained and the materials proportions areequal for each hand sheet. The paper making wire is placed on the screenin the box. The box is closed and water is added. Add 2.5 liters offiber dispersion to the box with agitation. Drain to form the sheet. Drysheet, using vacuum to remove excess water allow to air dry or add heatusing a print dryer, drum dryer, hot plate or other device. Apply heatabove the melt temperature of the sheath polymer of the bi-componentfiber.

A resin saturating procedure is used to saturate hand sheets with resinfor strength and durability. Place hand sheets on rack in the oven anddried at 300° F. (150° C.) for 10 minutes and then weighed to obtaininitial basis weight. Using resin formulation, select resin ingredientsand measure all of them into individual containers, then combine themwith water. Using a size press laboratory saturating system, adjust theupper roll pressure to 40 psi. Fill saturating pan with the resinsolution. Dip handsheet into resin pan and saturate it on both wire andfelt side. A support scrim for either wire, felt or both sides may beused in laboratory saturating to prevent sticking and improve handling.Remove the scrim, if used and place wet handsheet on rack in the ovenand dry it at 300° F. (150° C.) until dry, and then measure the basisweight. Calculate resin pick up (express as percent) using the formula:Resin pick up=(Saturated weight−Initial weight)·100/Initial weight

If resin pick up is different than target pickup level adjust resinconcentration in steps until target level is achieved. With the rightresin pickup level, saturate a batch of handsheets. Remove scrims ifused and place wet handsheets on racks allowing them to air overnight.Place dry dried sheets on racks in the oven at 300° F. (150° C.) for 10minutes, measure weight and calculate the final basis weight and theresin pickup. TABLE 3 Furnish Characteristics Efficiency Layer (% basedon dry weight) Basis Weight of dried layer 65 to 138 g-m⁻² Latex resinUp to 25% PVA binder fiber 0 to 2% PET/PET sheath core bi- At least 5%component binder fiber Glass fiber 50 to 95% Secondary polyester fiber 0to 55% Loading Layer Basis Weight of dried layer 33 to 65 g-m⁻² Latexresin Up to 25% PVA binder fiber 0 to 2% PET/PET sheath core bi- up to15% component binder fiber Glass fiber 70 to 90% Secondary polyesterfiber 0 to 25%

A second set of single layer hand sheets were prepared using thedisclosed procedure for testing. The furnish formulations are found inthe following Table 4. The polyvinyl alcohol (PVA) binder resin was usedat 1%. TABLE 4 Furnish information Furnish (dry weight %) Glass FiberFurnish A Furnish C Furnish D Furnish G (average diameter) (93 g-m⁻²)(93 g-m⁻²) (93 g-m⁻²) (93 g-m⁻²) GLASS FIBER 706  9%  9%  9% 11% (0.3micron) GLASS FIBER 40% 40% 40% 28% 110X (2 micron) GLASS FIBER 30% 30%39% 30% 112X (3 micron) GLASS FIBER 10% 10% — — Lauscha EC 6-6 SC (6micron) GLASS FIBER 10% — — — Lauscha EC 10-12 SC (10 micron) PVA (88% 1%  1%  1%  1% hydrolyzed) SPG 056-11 BICOMPONENT — 10% 20% 30% FIBER(DuPont 271P

TABLE 5 Handsheet Datasheet Target Dry Wet Resin Permeability, Tensile,Tensile, Dry Binder Pick- Weight, Thickness, ft- lbs/(in lbs/(in Burst,Loading, β @ β @ Furnish Type Fiber up g-m⁻² inches min⁻¹ width) width)psi gms-ft⁻² 10μ 75μ A base 0% 0% 109 0.031 27 2.2 0.9 8.6 8.5 4.15 6.98C base 10% 0% 101 0.030 29 2.4 1.3 8.4 8.7 4.66 7.76 D base 20% 0% 1030.052 31 1.4 0.8 8.5 10.6 5.17 8.95 G base 30% 0% 101 0.035 32 1.6 0.810.3 12.8 6.15 10.76 A saturated 0% 10% 124 0.033 23 6.5 5.7 8.5 5.33.75 6.41 C saturated 10% 10% 111 0.031 28 4.1 7.4 8.3 8.8 4.57 7.54 Dsaturated 20% 10% 112 0.051 29 4.2 3.1 8.3 8.6 5.34 8.80 G saturated 30%10% 111 0.035 31 10.9 10.6 15.2 9.9 5.93 9.77

Table 5 shows that in this experiment that the saturated hand sheets(e.g. Furnish D and G) have comparable permeability, β and loadingfiltration properties compared to the unsaturated version but haveimproved wet tensile strength.

FIG. 2 shows that testing conducted on handsheets of Table 5 (flatsheetmedia samples) using a miniflow Bench according to ISO 16889 teststandard. Base results show a 52% increase in loading using 30%bi-component fiber versus the control (0% bi-component).

FIG. 3 shows, in the hand sheets of Table 4, that saturated resultsprovide a 55% increase in loading using 30% bi-component fiber versusthe saturated control (0%).

FIG. 4 shows both base and saturated handsheet loading data using 0%bi-component with no resin as a control. This also highlights a keybenefit of using bi-component fiber; addition of saturate resin detractsfrom loading performance. If you compare the dry burst strength of thebase sheet with 30% bi-component fiber (10.3 psi) to the dry burststrength of the bi-component with and with saturate resin, you will seethat much more then 10% resin pick-up is needed to achieve the samestrength.

FIG. 5 is a cross sectional view of a spin on cartridge filter of theinvention. In FIG. 5, cartridge 50 is shown with an exterior shell 58,typically plastic or metallic.

At one end of the cartridge structure, is a contact surface end seal 59,a spin on threaded mounting means 60 including an outlet annular space52. The contact surface has inlet aperture 51 or liquid inlet 51 thatpermits a liquid having a potential particulate load to enter thecartridge 50. The cartridge contains pleated media 54 sealed at bothends using seal plates 56 and 55 to force the liquid through pleatedmedia 54 using liquid flow path 53. The pleated media material of theinvention 54 is typically mechanically insufficient to maintainfiltration properties without some form of support. The cartridge 50 ofthe invention supports pleated media 54 using a support layer 57 whichprevents the pleated media from collapsing under the force of the liquidpassing through the cartridge.

FIG. 6 shows one embodiment of a supported pleated media of theinvention. In FIG. 6, a pleated media 54 is shown supported on aperforate media support 61. The fluid flow 63 is shown wherein the fluidpenetrates the media and the perforate support into the interior of thestructure. The perforate media comprises apertures or pores 62 in thesupport to permit liquid flow from the exterior of the media to theinterior of the filter structure. The apertures or pores 62 aresurrounded by metal 61 maintaining a mechanically stable support toprevent collapse of the pleated media 54 FIG. 7 is a side view of thedown stream side of a screen supported media of the invention. In FIG.7, supported media 70 is shown wherein pleated media 54 is supported bya screen support 71. Generally to FIG. 6, fluid passes the media side ofthe supported media through the screen-supported side of the media tothe interior of the cartridge structure.

Test method ISO 16889 “Hydraulic Fluid Power Filters—Multipass Methodfor Evaluating Filtration of a Filter Element” was used to obtain theloading and β data. β results are reported per paragraph 12.6 in thistest method. β is a filter rating system used by the hydraulic industry.β_(x)=(number of particles>stated size upstream of the filter)/(numberof particles >stated size downstream of the filter). The “x” subscriptindicates the micron size of the particles. For example, if 1,000particles 15 micrometers and greater were counted upstream of thefilter, and 50 of those same size particles were counted downstream, theβ would be 20 or β₁₅=20. Stated another way, the filter is 95% efficienton particles 15 micrometers and larger. Testing conducted on handsheets(flatsheet media samples) using DCI Miniflow Bench according to ISO16889 test standard. Base results (see FIG. 2) show a 52% increase inloading using 30% bi-component fiber versus the control (0%bi-component). Permeability relates to the quantity of air(ft³-min⁻¹-ft-⁻² or ft-min⁻¹) that will flow through a filter medium ata pressure drop of 0.5 inches of water. In general, permeability, as theterm is used is assessed by the Frazier Permeability Test according toASTM D737 using a Frazier Permeability Tester available from FrazierPrecision Instrument Co. Inc., Gaithersburg, Md. or a TexTest 3300 orTexTest 3310 available from Advanced Testing Instruments Corp (ATI), 243East Black Stock Rd. Suite 2, Spartanburg, S.C. 29301, (864)989-0566,www.aticorporation.com. Pore size referred to in this disclosure meansmean flow pore diameter determined using a capillary flow porometerinstrument like Model APP 1200 AEXSC sold by Porus Materials, Inc.,Cornell University Research Park, Bldg. 4.83 Brown Road, Ithaca, N.Y.14850-1298, 1-800-825-5764, www.pmiapp.com.

Kahlbaugh et al., U.S. Pat. No. 5,082,476, disclose a filter designusing a depth media comprising a foam substrate with pleated componentscombined with the microfiber materials of the invention. Stifelman etal., U.S. Pat. No. 5,104,537, relate to a filter structure useful forfiltering liquid media. Liquid is entrained into the filter housing,passes through the exterior of the filter into an interior annular coreand then returns to active use in the structure.

Gillingham et al., U.S. Pat. No. 5,820,646, disclose a corrugated or Zfilter structure that uses a specific pleated filter design involvingplugged passages that require a fluid stream to pass through at leastone layer of filter media in a “Z” shaped path to obtain properfiltering performance. The filter media formed into the pleated Z shapedformat can contain the fine fiber media of the invention.

While the invention has been described in connection with specificembodiments thereof, the invention is capable of further modificationsand this application is intended to cover any variations, uses, oradaptations of the invention following the description of the inventionand including known or customary practice within the art to which theinvention pertains and as may be applied to the essential featureshereinbefore set forth and as follows in scope of the appended claims.

1. A filter medium comprising a layer comprising about 5% to 50 wt % ofa bicomponent binder fiber, about 50 to 95 wt % of a media fiber, about0.5 to 25 wt % of a binder resin, the layer having a basis weight ofabout 30 to 250 g-m⁻²; wherein the layer provides a permeability of 10to 40 ft-min⁻¹, and a wet bursting strength of about up to 50 lb-in⁻².2. The medium of claim 1 comprising a loading layer and an efficiencylayer.
 3. The medium of claim 2 wherein the loading layer has a basisweight of about 25 to 75 g-m⁻².
 4. The medium of claim 2 wherein theefficiency layer has a basis weight of about 50 to 150 g-m⁻².
 5. Themedium of claim 2 wherein the loading layer comprises about 1 to 25 wt %of a bicomponent binder fiber, about 70 to 90 wt % of a glass fiber. 6.The medium of claim 2 wherein the efficiency layer comprises about 5 to25 wt % of a bicomponent binder fiber, about 50 to 95 wt % of a glassfiber.
 7. The medium of claim 1 wherein the glass fiber comprises ablend of two of more glass fiber sources that differ by average diametereach source present in an amount of at least 2%.
 8. The medium of claim1 wherein the medium comprises about 50 to 80 wt % of a glass fiber. 9.The medium of claim 1 wherein the medium comprises about 1 to 20 wt % ofa binder resin.
 10. The medium of claim 2 wherein either the loadinglayer or the efficiency layer comprises about 0.5 to 55% of a secondaryfiber.
 11. The medium of claim 10 wherein the secondary fiber is apolyester fiber.
 12. The medium of claim 1 wherein the medium comprisinga wet bursting strength of about up to 30 lb-in⁻² and the mean flow poresize ranges from about 2 to about 10 micrometers.
 13. The medium ofclaim 1 wherein the medium comprises a mean flow pore size of about 4 toabout 8 micrometers.
 14. A filter efficiency medium comprising a layercomprising about 5 to 25 wt % of a bicomponent binder fiber, about 50 to95 wt % of a glass fiber, about 0.5 to 25 wt % of a latex resin, themedia layer having a basis weight of about 30 to 150 g-m⁻²; wherein thelayer provides a permeability of 10 to 40 ft-min⁻¹, a wet burstingstrength of about up to 50 lb-in⁻².
 15. The medium of claim 14 whereinthe glass fiber comprises a blend of two or more glass fiber sourcesthat differ by average diameter.
 16. The medium of claim 14 wherein theglass fiber comprises a blend of three or more glass fiber sources thatdiffer by average diameter.
 17. The medium of claim 14 wherein themedium comprises about 10 to 20 wt % of a bicomponent binder fiber. 18.The medium of claim 14 wherein the medium comprises about 50 to 80 wt %of a glass fiber.
 19. The medium of claim 14 wherein the mediumcomprises about 5 to 10 wt % of a binder resin.
 20. The medium of claim14 wherein the medium comprises a basis weight of about 60 to 140 g-m⁻².21. The medium of claim 14 wherein the medium comprising a wet burstingstrength of about up to 30 lb-in⁻² and wherein the mean flow pore sizeranges from about 2 to about 10 micrometers.
 22. The medium of claim 14wherein the medium comprises a mean flow pore size of about 2 to about10 micrometers.
 23. The medium of claim 14 wherein the glass fibercomprises a blend of a first fiber having an diameter of less than 0.5microns and a second glass fiber having a diameter of greater than 5microns.
 24. A filter loading medium comprising a layer comprising about1 to 15 wt % of a bicomponent binder fiber, about 50 to 90 wt % of aglass fiber, about 0.5 to 25 wt % of a latex resin, the media layerhaving a basis weight of about 25 to 75 g-m⁻²; wherein the layerprovides a permeability of 90 to 160 ft-min⁻¹, a wet bursting strengthof about up to 50 lb-in⁻².
 25. The medium of claim 24 wherein the glassfiber comprises a blend of two or more glass fiber sources that differby average diameter.
 26. The medium of claim 24 wherein the glass fibercomprises a blend of three or more glass fiber sources that differ byaverage diameter.
 27. The medium of claim 24 wherein the mediumcomprises about 5 wt % to 15 wt % of a bicomponent binder fiber.
 28. Themedium of claim 24 wherein the medium comprises about 70 to 90 wt % of aglass fiber.
 29. The medium of claim 24 wherein the medium comprisesabout 5 to 10 wt % of a binder resin.
 30. The medium of claim 24 whereinthe medium comprises a basis weight of about 30 to 60 g-m⁻²
 31. Themedium of claim 24 wherein the medium comprising a wet bursting strengthof about up to 30 lb-in⁻² and the mean flow pore size ranges from about2 to about 10 micrometers.
 32. The medium of claim 24 wherein the mediumcomprises a mean flow pore size of about 2 to about 10 micrometers. 33.The medium of claim 24 wherein the glass fiber comprises a blend of afirst fiber having an diameter of less than 0.5 microns and a secondglass fiber having a diameter of greater than 5 microns.
 34. A filtercartridge adapted for filtering particulate from a fluid, the filtercomprising: (a) a housing having an inlet and an outlet in fluidcommunication with the interior of the housing; (b) a filter mediaimposed in a filtration aspect between the inlet and the outlet, themedia medium comprising a layer comprising about at least 5% to 50 wt %of a bicomponent binder fiber, about 50 to 95 wt % of a media fiber,about 0.5 to 25 wt % of a binder resin, the layer having a basis weightof about 30 to 250 g-m⁻²; a permeability of 10 to 40 ft-min⁻¹ and a wetbursting strength of about up to 30 lb-in⁻²; and (c) and a perforatemechanical media support
 35. The filter of claim 34 wherein the mediumcomprises a loading layer having a basis weight of about 25 to 75 g-m⁻²and an efficiency layer having a basis weight of about 50 to 150 g-m⁻²,the loading layer comprises about 1 to 25 wt % of a bicomponent binderfiber, about 70 to 90 wt % of a glass fiber, the efficiency layercomprises about 5 to 25 wt % of a bicomponent binder fiber, about 50 to95 wt % of a glass fiber; wherein the filter provides a permeability of10 to 40 ft-min⁻¹, a wet bursting strength of about up to 30 lb-in⁻².36. The medium of claim 34 wherein the glass fiber comprises a blend oftwo or more glass fiber sources that differ by average diameter.
 37. Themedium of claim 34 wherein the glass fiber comprises a blend of three ormore glass fiber sources that differ by average diameter.
 38. The mediumof claim 34 wherein the medium comprises at least 5 wt % of abicomponent binder fiber.
 39. The medium of claim 34 wherein the mediumcomprises about 50 to 95 wt % of a glass fiber.
 40. The medium of claim34 wherein the medium comprises about 0 to 25 wt % of a binder resin.41. The medium of claim 34 wherein the medium comprises a basis weightof about 30 to 228 g-m⁻²
 42. The medium of claim 34 wherein the mediumcomprising a wet bursting strength of about up to 30 lb-in⁻²
 43. Themedium of claim 34 wherein the medium comprises a mean flow pore size ofabout 2 to about 10 micrometers.
 44. The medium of claim 34 wherein theglass fiber comprises a blend of a first fiber having an diameter ofless than 0.5 microns and a second glass fiber having a diameter ofgreater than 5 microns.
 45. A method of filtering a liquid the methodcomprises passing a liquid having a particulate load through a filtermedium comprising a layer 5% to 50 wt % of a bicomponent binder fiber,about 50 to 95 wt % of a media fiber, about 0.5 to 25 wt % of a binderresin, the layer having a basis weight of about 30 to 250 g-m⁻²; whereinprovides a permeability of 10 to 40 ft-min⁻¹, a wet bursting strength ofabout up to 50 lb-in⁻² and removing the particulate load.
 46. The methodof claim 45 wherein the medium comprises a first layer comprising aloading layer having a basis weight of about 25 to 75 g-m⁻² and a secondlayer comprising an efficiency layer having a basis weight of about 50to 150 g-m⁻², the loading layer comprises about 1 to 25 wt % of abicomponent binder fiber, about 70 to 90 wt % of a glass fiber, theefficiency layer comprises about 5 to 25 wt % of a bicomponent binderfiber, about 50 to 95 wt % of a glass fiber.
 47. The method of claim 45wherein the liquid is an aqueous liquid with a particulate load.
 48. Themethod of claim 45 wherein the liquid is a non-aqueous liquid with aparticulate load.
 49. The method of claim 45 wherein the liquidcomprises a fuel.
 50. The method of claim 45 wherein the liquidcomprises a lubricant.
 51. The method of claim 45 wherein the liquidcomprises a hydraulic fluid.
 52. The method of claim 45 wherein theliquid comprises a brake fluid.
 53. The method of claim 46 wherein theglass fiber comprises a blend of two or more glass fiber sources thatdiffer by average diameter.
 54. The method of claim 45 wherein the glassfiber comprises a blend of three or more glass fiber sources that differby average diameter.
 55. The method of claim 45 wherein the mediumcomprises about 50 to 95 wt % of a glass fiber.
 56. The method of claim45 wherein the medium comprising a wet bursting strength of about up to30 lb-in⁻².
 57. The method of claim 45 wherein the medium comprises amean flow pore size of about 2 to about 10 micrometers.
 58. The mediumof claim 46 wherein the glass fiber comprises a blend of a first fiberhaving an diameter of less than 0.5 microns and a second glass fiberhaving a diameter of greater than 5 microns.